Citation and License

BMC Evolutionary Biology 2011, 11:221
doi:10.1186/1471-2148-11-221

Published: 26 July 2011

Abstract

Background

Metacrangonyctidae (Amphipoda, Crustacea) is an enigmatic continental subterranean
water family of marine origin (thalassoid). One of the species in the genus, Metacrangonyx longipes, is endemic to the Balearic islands of Mallorca and Menorca (W Mediterranean). It
has been suggested that the origin and distribution of thalassoid crustaceans could
be explained by one of two alternative hypotheses: (1) active colonization of inland
freshwater aquifers by a marine ancestor, followed by an adaptative shift; or (2)
passive colonization by stranding of ancestral marine populations in coastal aquifers
during marine regressions. A comparison of phylogenies, phylogeographic patterns and
age estimations of clades should discriminate in favour of one of these two proposals.

Results

Phylogenetic relationships within M. longipes based on three mitochondrial DNA (mtDNA) and one nuclear marker revealed five genetically
divergent and geographically structured clades. Analyses of cytochrome oxidase subunit
1 (cox1) mtDNA data showed the occurrence of a high geographic population subdivision in
both islands, with current gene flow occurring exclusively between sites located in
close proximity. Molecular-clock estimations dated the origin of M. longipes previous to about 6 Ma, whereas major cladogenetic events within the species took
place between 4.2 and 2.0 Ma.

Conclusions

M. longipes displayed a surprisingly old and highly fragmented population structure, with major
episodes of cladogenesis within the species roughly correlating with some of the major
marine transgression-regression episodes that affected the region during the last
6 Ma. Eustatic changes (vicariant events) -not active range expansion of marine littoral
ancestors colonizing desalinated habitats-explain the phylogeographic pattern observed
in M. longipes.